1. Field of the Invention
The present invention relates to a positioning method using a mobile terminal and a mobile terminal having a positioning function, and more particularly, to a positioning method using a mobile terminal which performs positioning by communicating information among a plurality of mobile terminals, and a mobile terminal having a positioning function.
2. Description of the Related Art
In recent years, mobile terminals such as a personal digital assistant (PDA), a portable telephone and the like have implemented a function of positioning for these mobile terminals.
Conventionally, as illustrated in FIG. 1, when a mobile terminal 1 performs positioning, a positioning apparatus 2 in an existing positioning system typically undertakes the positioning, and supplies resulting position information to the mobile terminal 1.
For example, a typical one of existing positioning systems is a global positioning system (GPS). The GPS comprises a plurality of artificial satellites orbiting the earth, each of which emits a positioning signal which has temporal information multiplexed with satellite position information. On the earth, the positioning signals from the plurality of GPS satellites are received to calculate times required for radio waves to reach from the respective satellites, and calculate the distances from the respective satellites for the positioning. The GPS features in its service area globally covering the entire earth and extremely high positioning accuracy.
Another existing positioning system employs a method of positioning a mobile terminal, when it is a portable telephone, using information such as the position of a base station connected to the portable telephone, a received field strength, and the like.
In addition, a simple positioning method involves receiving signal from a position information beacon apparatus, which has been previously installed at a fixed location, to acquire position information from the received signal.
The conventional positioning systems and methods for mobile terminals as described above, however, have problems as follows:
(1) The positioning method which acquires position information using the GPS requires sufficiently open sky at a site at which the positioning is performed, due to the nature of the GPS that receives signals emitted from satellites to acquire the position information based on received signals. If any object exists and blocks signals from the satellites, falling down from the sky, the positioning system is prevented from correctly receiving the signals emitted from a number of satellites required for the positioning. A failure in correctly receiving the signals emitted from the number of satellites required for the positioning would result in a deteriorated positioning accuracy. Particularly, if the number of satellites from which signals are received is three or less, the positioning itself becomes difficult to achieve.
However, the open sky is not always available at a site at which the positioning is required. Specifically, the positioning is often required within buildings, and in urban areas surrounded by buildings. For the reason set forth above, only a GPS positioning apparatus equipped in a mobile terminal would encounter difficulties in achieving the positioning within a building, and in an urban area surrounded by buildings.
(2) The positioning method using information such as the position of a base station connected to a portable telephone, which serves as a mobile terminal, a received field strength, and the like, suffers from a low positioning accuracy, and also encounters difficulties in achieving highly accurate positioning within a building or the like, as is the case with the positioning method utilizing the GPS.
(3) The positioning method which acquires position information by receiving a signal from a position information beacon apparatus previously installed at a fixed location is incapable of achieving the positioning at a site at which no beacon apparatus is installed.